The production of insulation materials from fibers, for example fibers of wood, of flax, of hemp or of wool or the like, if appropriate with the addition of thermo-plastic binder fibers, is known. The production of these insulation materials and fleeces is carried out by the dry method, for example by means of aerodynamic fleece folding methods with a spatial orientation of the fiber/binder fiber matrix in a drum opening and distributing the fiber stock and with a subsequent thermal consolidation of the fiber/binder fiber matrix in a hot-air throughflow dryer. This is described, for example in DE 100 56 829 A1.
Where wood fiber insulation materials are concerned, the production of the insulation materials boards may also be carried out by the wet method with a subsequent hot-pressing method.
In the previous methods for the production of insulation materials from natural and synthetic fibers, there is still often an insufficient spatial orientation of the wood fibers and binder fibers. On account of the predominantly parallel orientation of the fibers, these insulation material boards can easily be split perpendicularly to the surfaces of the board in spite of thermal consolidation in the hot-air throughflow dryer. Moreover, the compressive strength of these insulation material boards is relatively low because of the low bulk density.
The result of this is that the use of such boards as insulation material and plaster base, particularly on the outside, presents problems, since the insulation materials having low compressive strength and low transverse tensile strength have to be fastened to the substrate by special fastening means. Moreover, too low a compressive strength has an adverse effect on the impact resistance of the composite heat insulation system.
To achieve a sufficient structural strength of the insulation material board, binder fibers are used, which, as a rule, consist of a polyester or of a polypropylene core with thicknesses of 2.2 to 4.4 detex in which are added in a proportion of up to 25 percent by weight. Since the costs of these binder fibers are relatively high in comparison with wood fibers, such insulation materials are comparatively costly. Furthermore, the addition of binder fibers has only a limited improving effect in increasing the compressive strength. An optimum bulk density for a wood fiber board as a plaster base board is approximately 100 kg/m3. Higher bulk densities have an adverse effect on the thermal conductivity of the insulation plate, in such a way that the required thermal conductivity group WLG 040 is not achieved, but, on the other hand, increased stability is achieved.